(a) Field of the Invention
The present invention relates to an automatic transmission for vehicles, and more particularly, to a planetary gear train of an automatic transmission for vehicles, which improves a power transmission capability and enhance fuel efficiency by implementing at least ten forward shifts by using a minimum number of components and reduces driving noise of a vehicle using an operating point at a low revolutions per minute (rpm) region of an engine.
(b) Description of the Related Art
In general, in an automatic transmission field, a technology for improving fuel efficiency of a vehicle and maximizing drivability has been researched by increasing the number of shift stages of the transmission. Additionally, recent increase in oil price is a factor causing competition for enhancement of the fuel efficiency. As a result, in the case of an engine, research for reducing a weight and enhancing the fuel efficiency through downsizing has been conducted and in the case of an automatic transmission, research to secure both drivability and fuel efficiency competitiveness through increased shift-stages has been conducted.
However, in the case of the automatic transmission, as the number of shift-stage increases, the number of internal components, in particular, the number of planetary gear sets increases and the whole length of the transmission thus increases. Therefore, mountability and production cost, a weight, and power transmission efficiency may still deteriorate. Accordingly, in the case of the automatic transmission, development of a planetary gear train achieving maximum efficiency with a minimal number of components is important to increase a fuel efficiency enhancement effect through the increased shift-stages of the transmission.
In this aspect, in recent years, the automatic transmission has been configured to implement transmission of eight-speed or more to be mounted on the vehicle and research and development of a planetary gear train capable of implementing a shift-stage of eight speeds or more have also been continuously required. However, most general automatic transmissions of eight speeds or more are constituted by 3 to 4 planetary gear sets and 5 to 6 control elements (friction elements) and thus, the whole length of the system increases, and as a result, the mountability may deteriorate. As a result, to form the shift-stage of the automatic transmission into the multi-stages, in recent years, a double row structure that arranges the planetary gear set on the planetary gear set has been adopted or a dog clutch has been applied instead of a wetting control element, but in this case, an applicable structure is limited and deterioration of a shift quality due to the application of the dog clutch may occur.
The above information disclosed in this section is merely for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.